A packaging bag into which a material to be packaged, for example, a liquid, powder or a viscous material is filled, the resultant bag being then sealed up has heretofore been formed generally by sealing vertically and laterally three or four sides of a packaging film made of packaging material, such as a film of a synthetic resin or a laminate formed by bonding the same film of a synthetic resin as mentioned above and aluminum foil together.
As an example of a machine for obtaining such a packaging bag, a filling and packaging machine for making three-side-sealed packaging bags will be described by using FIG. 10 and FIG. 11. Referring to the same drawings, a retainer frame 2 is provided at one side of a machine base 1 of the filling and packaging machine, and a raw film roll R made of a rolled film F mounted on this retainer frame 2 is detachably and replaceably retained on the retainer frame 2. On an upper portion of the machine base 1, a film guide mechanism 3 and a film folding mechanism 4 are provided. On a front side portion of the machine base 1, a vertical sealing mechanism 5, a lateral sealing mechanism 6 and a cutter mechanism 7 are provided in the mentioned order from the upper side. The packaging film F is introduced via the film guide mechanism 3 onto the film folding mechanism 4. The film F is folded vertically in two by the film folding mechanism 4. The resultant film is fed as the film F while being held between left and right vertical seal rolls 5A provided in the heated vertical sealing mechanism 5. The film F is heat sealed with the vertical sealing rolls 5A so that the film F is cylindrically and vertically sealed FH. The film F is then heat sealed laterally with left and right lateral seal rolls 6A provided in the heated lateral seal mechanism 6 so that the film F is laterally sealed FS. Owing to this lateral sealing FS, a bottom portion constituting a packaging bag P is formed. Into a bottomed cylindrical film F thus formed, a material M to be packaged made of a liquid and the like is filled by, for example, a filling nozzle 8A of a filling mechanism 8. The film F is further fed and laterally sealed FS again at a bag-mouth portion of the film F with the lateral seal rolls 6A of the lateral sealing mechanism 6, the material W to be packaged being thereby sealed to form continuous packaged bags P. Intermediate portions of the laterally sealed FS zones of the continuous packaged bags P are cut with a cutter mechanism 7, and the packaged bags P are sent out in an individually separated state. A filling and packaging machine thus formed is known.
In the case of this machine, the above-mentioned lateral sealing mechanism 6 includes two pairs of sealing rolls, i.e. lateral sealing rolls 6A of the first lateral sealing mechanism 6 and those 6A of the second lateral sealing mechanism 6 provided in a vertically separated state. The material W to be packaged filled into the film F fed as the film F is formed into a cylindrical bag by the filling nozzle 8A of the vertical filling mechanism 8 is heat sealed laterally FS with the two lateral sealing rolls 6A, which are provided in the first lateral sealing mechanism 6, as the material W is forced out with the film F pressed in a sandwiched state by these lateral seal rolls. The portion FS laterally heat sealed with the lateral sealing rolls 6A of the first lateral seal mechanism 6 is pressed again by the lateral sealing rolls 6A of the second lateral sealing mechanism 6 in a low-temperature overheated condition or in a normal temperature condition so as to keep excellent the sealed condition of the laterally sealed FS portion.
In the above-described related art filling and packaging machine, the film F is fed as the film is heat sealed with a pair of vertical sealing rolls 5A of the vertical sealing mechanism 5. When a rotational speed of the two vertical sealing rolls 5A provided in the vertical sealing mechanism 5 is low, the contact time of the vertical sealing rolls 5A and film F becomes long, so that the heat of the vertical sealing rolls 5A is transmitted in a proper condition to a thermally fusible resin layer of the film F, which is then thermally melted. Therefore, the heat is transmitted in a proper condition to the vertical sealing FH portion of the film F, which is thereby melted. Accordingly, the proper heat sealing can be carried out on the vertical sealing FH portion of the film F. Since the region of the film F held between, pressurized by, and heat sealed with a pair of vertical sealing rolls 5A becomes a narrower region Ti as shown in a schematic diagram of FIG. 11, in inverse proportion to the transfer speed of the film F since the region of the film F held between and heated with the two vertical sealing rolls 5A is disposed in a plane in which the circular vertical sealing rolls 5A are positioned in an abutted state with respect to the film F. As a result, a shortage of the quantity of heat occurs in the portion of the film F which is on the forward side thereof with respect to the direction of the rotation thereof and in the portion of the film F which is on the rearward side thereof with respect to the same direction, and imperfect heat sealing occurs in some cases in the vertical sealing FH portion contacting these two portions.
Under the circumstances, a filling and packaging machine, in which these points are taken into consideration has been proposed [refer to, for example, JP-A-2001-72019 (Publication 3 to 4 pages, FIG. 1 and FIG. 2)] which is provided with a preheating mechanism 11 between the upper side of a vertical sealing mechanism 5, i.e. a film folding mechanism 4 on the upstream side in the transfer direction of a film F and the vertical sealing mechanism 5, the preheating mechanism 9 being positioned between both edges of the film F folded in two, to preheat end portions of both edges of the film F, for the purpose of making up for the shortage of the quantity of heat occurring while the film is heat sealed as the film is pressurized by the vertical sealing mechanism 5.
However, the means for preheating the film F, which is made of a preheating mechanism 11 provided in the related art filling and packaging machines including that disclosed in JP-A-2001-72019 employs a structure for heating the film F by bringing the edge portions only of the folded film F into contact with the preheating mechanism 9. Therefore, contact regions with respect to the preheating mechanism 9 are small, so that the film F is partially heated. In consequence, the heat of the heated portions propagates and escapes to the surrounding portions of the film F, so that it cannot be said that the preheating effect is excellent. This poses a problem of necessarily setting high the preheating temperature of the preheating mechanism 11, and there is also the possibility that a fused layer on the inner side of the film F is melted and damages the film F. This phenomenon would occur noticeably in the structure disclosed in JP-A-2001-72019 in which a preheating mechanism is provided on the inner side of a film to be folded.
Other conceivable preheating means include a preheating means in which heaters are contained, for example, in rollers for feeding the film F, and the film is fed out as the film F is held tightly between the heated rollers or as predetermined tension is exerted thereon. Thus, the film F heated with the preheating means made of rollers is sent into the film folding mechanism and folded in two, and the film F is then sent into a vertical sealing mechanism. When the heated film F is sent into the film folding mechanism, friction is liable to occur between a guide of the film folding mechanism and film F, though the degree of the friction differs depending upon the kind of the material of the film F. There is the possibility that the film F meanders due to an increase in the level of the friction.
As filling and packaging machines formed with these points taken into consideration, the applicant of the present invention has proposed filling and packaging machines in which a preheating means is added to a film folding mechanism disclosed in, for example, JP-A-2002-104310 etc.
In the filling and packaging machine disclosed in JP-A-2002-104310 etc., the film is preheated in the widthwise direction thereof, so that the film as a whole folded in two is fed out as the film is heated. Therefore, the film is sent in a preheated state while maintaining the non-heat-losing effect to a vertical sealing point in which a subsequent step is started. This solves the problems encountered in the above-mentioned related art (JP-A-2001-72019) filling and packaging machine. However, since it is generally necessary to introduce the film from the upper guide rolls while folding up the film in two so that the film is squeezed, the preheating means for pressing the film from the outside tends to tangentially contact in the widthwise direction. In the invention disclosed in JP-A-2002-104310, the film as a whole is preheated in the widthwise direction thereof. Therefore, when the film feeding speed is comparatively low, the heat is transmitted comparatively well to the film, and a good preheated condition of the film can be maintained. A heat transfer rate tends to lower in inverse proportion to the film feeding speed, and, therefore, it is conceivable that a shortage of the quantity of heat is brought about due to the film preheating operation.
Under the circumstances, the present invention aims at providing a filling and packaging machine formed with attention paid to these problems, and capable of making up for a shortage of the quantity of heat occurring when a film is heat sealed as the film is pressurized by a vertical sealing mechanism without causing a packaging rate to lower.